In order to increase the degree of effeciency of various processes, for example in the manufacture of sulphate pulp, it is necessary to preheat a thick liquor to high temperature prior to its combustion in a recovery boiler. The preheating is carried out by steam in a heat exhanger, which is a tube heat exchanger. Due to the high temperature, however, the tubes are incrusted with matter and impurities contained in the thick liquor.
The heat exchanger, therefore, must be opened at regular intervals to clean the tubes in order to maintain a somewhat uniform degree of efficiency. This cleaning work most often must be carried out in a hot and inconvenient atmosphere and it also adds extra costs to the process. In order to prevent interruption of the operation during the cleaning work, the heat exchanger can be doubled so that one heat exchanger is operative while the other one is being cleaned. Interruptions of the operation as well as extra heat exchangers increase the operation expenditures of the plant.
The present invention renders it possible to keep the hot surfaces wetted by the thick liquor clean of incrusting matter and thereby to maintain a uniform degree of efficiency of the heat exchanger without the process having to be stopped. It is, of course, possible to utilize the invention in other connections where there is a requirement of repeated cleaning of the heat exchanger surfaces.